Implement master client for reading training tasks

Add documentation for installing Go when building Paddle manually

update rnn doc from v1-api to v2-api.

Abstract BBox and provide general functions

Fix pserver cmake

Parameter initializer in V2 API

Use CMAKE_CURRENT_BINARY_DIR instead of CMAKE_BINARY_DIR to make it more portable (when paddle is used as subdirectory)

User can provide an initializer in ParamAttr. The initializer will be called when at parameters.create().

new parameterupdater use paddle pserver cclient of go

implement master server client, remove unnecessary dummy variable

Modify pserver client C API, create better test.

Add convert function